The present invention relates to a low-noise receiving amplifier and down converter system for coupling an antenna to a receiver. It is particularly intended for coupling microwave antennas of the type used to receive satellite signals in the microwave frequency range.
Coupling circuits for microwave antennas operate in the 1 GHz to 40 GHz range. The signal from the satellite must be received and down converter to a frequency which is compatible with a conventional satellite receiver. Such satellite signals are typically very low power (typically 5 Watt peak) and there is a fairly high loss between the satellite and the receiving station.
Antenna coupling circuits generally include some type of receiving amplifier for amplifying the signal above the thermal background noise and a down converter comprising a mixer and local oscillator for tuning and converting the frequency down to an intermediate frequency which can be accepted by the conventional receiver, for example a television or satellite receiver.
U.S. Pat. No. 4,429,417 of Yool shows one system for amplifying and converting microwave signals of this type. An integrated amplifier and converter circuit is mounted on the microwave antenna. The circuit must be matched or tuned to the antenna input signal and this is done by means of several fixed inductors. Thus, the circuit will not be perfectly matched if there is a slight change in the signal, and it must be set up in advance for the particular antenna used.